Doctoral defence: Stênio Ítalo Araújo Foerster "Phylogenetic comparative studies of body size in insects and arachnids: from predictions to applications"

Stênio Ítalo Araújo Foerster will defend his doctoral thesis "Phylogenetic comparative studies of body size in insects and arachnids: from predictions to applications" for obtaining the degree of Doctor of Philosophy (in Zoology and Ecology) on 17 October at 10:15 .

Supervisors: Professor Toomas Tammaru, University of Tartu, and Research Fellow John Clarke, German Centre for Integrative Biodiversity Research (Germany)

Opponent: Professor Matjaž Kuntner, National Institute of Biology (Slovenia)

Summary: Body size is one of the most important traits in animals, influencing how they move, reproduce, and interact with their environment. Yet, for many arthropods like insects and arachnids, body size can be difficult to measure directly, especially when dealing with hundreds of individuals, or when the specimens are damaged. One way to facilitate the measuring is to use allometry, which defines the mathematical relationships that link body size to simpler measurements of body parts, such as wingspan in a flying insect or the size of a body segment in an arachnid. With this approach, scientists can reliably estimate body size from specimens that are old, poorly preserved or incomplete, and even from fossils.

In my doctoral research, I developed and tested allometric models to predict body size in two diverse groups: geometrid moths and buthid scorpions. By combining phylogenetic methods with large datasets, I identified which measurements best predict body size and then applied these predictions to study ecological and evolutionary aspects in each group.

For moths, maximum wingspan was the best predictor of dry body mass, and models were more accurate when combined with measurements of abdomen width. Based on body size predictions, I found that larger moths generally overwinter as larvae and have broader diets.

In scorpions, the length of the fifth “tail” segment predicted total length most effectively, while telson length (the segment that carries the sting) best predicted carapace length. These models worked across sexes and even beyond the studied family. I also found that in Neotropical buthids, females tend to be larger, but males often have proportionally bigger structures linked to reproduction.

This work shows that phylogenetically informed allometric models are powerful tools for estimating body size in invertebrates. They open the door to studying ecological and evolutionary aspects in groups where direct measurements are often impractical or even impossible.

The defence will be held in room 127 of Oecologicum and via Zoom (meeting ID: 949 1445 3281, passcode: 592404)